In general, noise barriers are built on a road or railroad near a residential region, on various facilities generating severe noise, or in the vicinity of construction sites generating severe construction noise, and serve to block noise and vibration.
Noise barriers are typically classified into a sound-blocking type, a sound-absorbing type, and a resonance type according to functions thereof The sound-blocking noise barrier includes a transparent noise barrier made of polycarbonate or polyacrylics, a compression molding cement panel, a plastic panel, etc. The sound-absorbing noise barrier includes a metallic noise barrier made of aluminum and galvanized steel sheets, a wooden noise barrier using preserved wood, a lightweight concrete noise barrier, etc.
Among these noise barriers, the sound-absorbing noise barrier employs a porous material such as glass fiber, polyester (PET), and the like to have sound-absorbing effects. Such a porous sound-absorbing material has high sound-absorbing performance in a high frequency band, but exhibits negative sound-absorbing performance in a low frequency band. Further, the porous sound-absorbing material has a large thickness to achieve high sound-absorbing performance, and must be combined with another material for interior decoration.
Further, since polyester absorbs water, its surface is subjected to water-repellent finishing in preparation for rainy weather, but the water-repellent finishing has a problem of decreasing a sound-absorbing coefficient. Further, glass wool or Rockwool is coated with a film to prevent scattering or the like on the surface thereof, but the coated film decreases the sound-absorbing coefficient.
The metallic noise barrier is likely to be corroded and discolored due to exhaust fumes and rainwater. The wooden noise barrier generally employs preserved wood and thus can suffer from surface contamination, cracking or discoloring when used for a long period of time.